1. Field of the Invention
The present invention relates to a technology for limiting an electric current applied to a motor driver within a tolerance.
2. Description of the Related Art
A conventional method for protecting a motor driver employs detection of a temperature of the driver or detection of a drive current applied to the driver to prevent a flow of an overcurrent into the driver. According to a motor control device disclosed in Japanese Patent Application Laid-open No. 2005-80349, an overcurrent protecting circuit and a heat protecting circuit are included in an inverter circuit to protect switching elements of the inverter circuit.
Moreover, according to a technology disclosed in Japanese Patent Application Laid-open No. 2004-229430, when an overcurrent is detected, a signal indicating that a motor stops rotating due to the detection of the overcurrent in an overcurrent protecting circuit of the inverter circuit is output with a signal indicating the number of revolutions of the motor, so that an external microcomputer can determine whether an overcurrent is applied to the inverter circuit.
In this manner, in the conventional technologies for protecting the driver, an overcurrent determining circuit is provided to the driver. The overcurrent determining circuit determines whether an overcurrent is applied to the driver with a comparator that compares a current with a predetermined current limit. If the current exceeds the current limit, the overcurrent determining circuit determines that an overcurrent is applied to the driver.
Therefore, in the conventional technologies, it is necessary to include the comparator inside the motor control device. However, a power consumption increases because of a current sensing resistor of the comparator, and thus the efficiency decreases. Furthermore, in the conventional technologies, it is not possible to change setting of the current limit. Moreover, the conventional motor control device costs due to the comparator and the increased number of control integrated circuits (IC) and pins for the comparator.